A light emitting diode (LED) is a semiconductor element converting electric energy to light such as ultraviolet light or visible light to radiate the light, and a LED lamp in which such a LED chip is sealed by, for example, transparent resin is used in various fields. To realize a visible-light LED lamp, a LED chip having a light emitting layer made of GaP, GaAsP, GaAlAs, GaN, InGaAlP, or the like is used. To use, as a light source, a light emitting semiconductor element such as a laser diode instead of the light emitting diode has been also considered.
Being semiconductor elements, a light emitting diode and a laser diode have advantages that they have long life and high reliability, and when they are used as a light source, an exchange work is lightened. Therefore, LED lamps using, for example, a LED chip are widely used in industrial application as backlights, various switches, and so on in displays such as liquid crystal displays in mobile communication equipment, PC peripheral equipment, OA equipment, household electric equipment, and so on, and also used in general lighting application.
Color tone of light radiated from a LED lamp depends not only on emission wavelength of a LED chip. For example, phosphors contained in transparent resin sealing a LED chip can provide lights in a visible light spectrum from blue to red according to an intended use. Further, a function of reproducing subtle color tone with higher definition has recently been requested of various displays. Accordingly, there is a demand for enabling one LED lamp to emit white light and lights in various neutral colors.
In particular, LED lamps emitting white light have rapidly come into wide use as backlights of liquid crystal displays, vehicle lamps, and the like, and their application range is expected to greatly expand as substitutes for fluorescent lamps in future. As white light emitting LED lamps currently in actual or experimental use, there have been known a lamp in which blue emitting LED chip and a yellow emitting phosphor (YAG), and further a red emitting phosphor are combined, and a lamp in which an ultraviolet emitting LED chip and a mixture of blue, green, and red emitting phosphors are combined (for example, see Patent Documents 1, 2).
The former white LED lamp is more widely used at present than the latter white LED lamp because the former is superior in brightness characteristic and so on to the latter. However, the former has a disadvantage that the emitted light appears yellowish depending on a line of sight, and unevenness of yellow and white appears when the light is projected onto a white surface. For this reason, emission color of the former white lamp is sometimes called pseudo white. On the other hand, the latter white LED lamp using the ultraviolet emitting LED chip has an advantage that it can provide emitted light and projected light with small unevenness, though being inferior in brightness to the former. For this reason, the latter white LED lamp is expected to be a mainstream of white lamps for lighting use in future, and the development thereof is rapidly progressing.
In the course of the development of the white LED lamp using the ultraviolet emitting LED chip, it has been found out that unevenness in emitted light and projected light also occurs in a white LED lamp in which an ultraviolet emitting LED chip and plurality of phosphors different in emission color are combined, even though a degree of the unevenness is not as high as that in a white LED lamp using a blue emitting LED chip. It has been also found out that a phenomenon occurs that light leaking from a side face of the LED lamp (side leakage light) has color different from intended white color. Such a phenomenon (nonuniformity of light) is not preferable in using the LED lamp in a lighting device and the like, and causes deterioration in quality and characteristic thereof.    Patent Document 1: JP-A 2000-073052 (KOKAI)    Patent Document 2: JP-A 2003-160785 (KOKAI)